Conservatives seem to have grown bored with predicting an election day slaughter and have already moved on to gloating in advance over said slaughter. Rich Lowry and Ramesh Ponnuru have a story in National Review rubbing in the demise of the Democrats' electoral coalition:
The trends seemed to be Democrats’ friends. A rising nonwhite population; an increasingly unchurched youth; a growing tendency of college-educated voters to back Democrats: If demography was destiny, the Republicans’ fate looked bleak. To add to conservatives’ misery, the country was in the midst of a financial crisis widely blamed on deregulation.
And Jay Cost in the Weekly Standard says that Obama's program has failed, thus splintering his electoral coalition:
Ever since the conservative wing of the Republican party triumphed in 1980, liberal analysts have been warning the GOP that it must moderate if it is to survive. The most recent iteration of this argument is the “emerging Democratic majority” theory, long promulgated by John Judis of the New Republic and Ruy Teixeira of the Center for American Progress, which has ties to the Obama administration. In essence, their theory holds that demographic, social, and economic changes will move the country back to the center-left. They saw the 2008 presidential election as the first of many victories for this new majority. ...
the Reagan Revolution lasted as long as it did because of the tremendous prosperity of the 1980s. In each instance, the president who pulled off the realignment did so by contrasting his record of successful governing with the failures of his opponents.
This essential ingredient is missing for Obama in 2010. The president’s economic policy has broadly been judged not to have succeeded, and his health care law may be the most unpopular significant legislation in 100 years. Voters still look negatively upon the record of President George W. Bush, and they still would like to see President Obama succeed, but they do not believe the country has turned a corner. If it doesn’t recover before the 2012 election, President Obama will have a difficult time reconstituting his electoral coalition—while Republicans, if they play their cards right, will enjoy a terrific opportunity to consolidate their midterm gains.
I'm sure you can find somebody who predicted after 2008 that the Democrats would never have a bad election again. But that's not a serious iteration of the Emerging Democratic Majority thesis iterated by Judis and Teixiera. The serious argument is that the demographics of the national electorate are slowly moving in the Democrats' direction. The minority share of the electorate is growing. And younger generations of voters are considerably more liberal than older generations, and the ideological/partisan affiliations of voters tend to stay relatively constant over time.
Now, short-term factors often overwhelm these long-term trends. It's going to get colder between today and January 1st, but any given day could easily be warmer than the day before, and sometimes a lot warmer. The 1946 election came in the middle of a period of overwhelming Democratic dominance, but that was a year Republicans cleaned up. Likewise, the 2010 election is a midterm election -- and midterm electorates tend to be older than presidential-year electorates -- in which Democrats control the whole government in the midst of the greatest economic crisis since the Depression. None of this belies the long-term demographic trends slowly pushing the country leftward.
Now, has Obama's agenda backfired and made young voters more conservative? Hardly:
In polls of the overall electorate, self-identified conservative frequently account for twice the number of liberals, even in years Democrats do well. (Democrats compensate for the lower share of liberals by winning strong majorities of moderates.) That is to say, a young cohort with more liberals than conservatives is a cohort that's vastly more liberal than the country as a whole.
There are some decent criticisms to be made of the Emerging Democratic Majority thesis. The best is that, as the electorate slowly gets more liberal, the Republicans will adjust and move to the center -- it's more of an emerging center-left majority than an emerging Democratic majority. The Emerging Democratic Majority actually came out shortly before the electorate was temporarily reshaped by the 9/11 attacks. The authors endured quite a bit of ridicule before subsequent elections eventually began to bear out their argument.
In American politics, there's no such thing as an unbeatable majority. Short-term factors like wars, scandals, and the economy overwhelm everything else. But the basic premise of an electorate slowly, slowly moving leftward remains as true as ever.